1. Field of the Invention
The present invention relates to a method of producing a surface-mount inductor, and a surface-mount inductor produced by the method.
2. Description of the Background Art
Currently, a surface-mount inductor is widely used which has a structure where a coil is encapsulated by an encapsulation material containing a magnetic powder and a resin. As a conventional technique of producing a surface-mount inductor, there has been known a surface-mount inductor production method using a lead frame, as disclosed, for example, in JP 2003-290992A. In this method, opposite ends of a coil are joined to a lead frame by resistance welding or the like. Then, the entire coil is encapsulated by an encapsulation material to obtain a molded body. A portion of the lead frame exposed from the molded body is subjected to shaping, such as bending, to form an external electrode.
Recent technical innovation in downsizing and functional upgrading of electronic devices is remarkable. In connection therewith, electronic components, such as a surface-mount inductor, are required to achieve higher performance, smaller size and lower cost. However, the conventional method using a lead frame involves a problem of a large material loss in the lead frame, which becomes a factor causing an increase in cost. Moreover, even if the ends of the coil are joined to the lead frame by means of resistance welding or the like, the joined portion between the lead frame and each of the ends of the coil is likely to be separated from each other due to a springback phenomenon in the coil.
Therefore, there has been proposed a method intended to subject opposite ends of a coil to shaping to form an external electrode, as disclosed, for example, in JP 2003-282346A and JP 2005-294461A. In a method disclosed in the JP 2003-282346A, a pair of upper and lower mold dies are used. A coil is fixed by clamping opposite ends (lead-out terminals) of the coil between terminal clamping portions of the pair of upper and lower mold dies. However, in a process of producing a small-sized surface-mount inductor, a diameter of a wire for use as the coil has to be set to a relatively small value in order to obtain a required number of turns. In this case, if the wire diameter is excessively small, it is difficult to fix the coil only through the ends thereof. Thus, this method is hardly used to produce a small-sized surface-mount inductor. Moreover, in this method, it is necessary to change dimensions of the terminal clamping portion of each of the mold dies depending on a diameter of a wire for use as the coil in each case.
In a method disclosed in the JP 2005-294461A, opposite ends of a coil are bent downwardly. The coil is placed within a mold die assembly in such a manner that an outer surface of each of the ends is brought into contact with an inner surface of the mold die assembly. An encapsulation material is charged into the mold die assembly to allow the coil to be buried in the encapsulation material. However, in this method, the ends have to be formed to support a wound portion of the coil while keeping a hollow space therebetween. Therefore, the ends of the coil are required to have a certain level of strength. If the coil is formed of a relatively thin wire, the strength of the ends of the wire becomes insufficient to cause difficulty in supporting the wound portion while keeping a hollow space therebetween. Moreover, displacement or deformation of the coil is likely to occur during the operation of charging the encapsulation material. Thus, this method is hardly used to produce a small-sized surface-mount inductor.